Chemical amplification positive resist compositions are materials for forming patterns on substrates. Specifically, when irradiated with radiation including far ultraviolet light, such a resist composition generates an acid in the irradiated areas, and undergoes reaction utilizing the acid as a catalyst to cause a difference in solubility in a developer between the areas unirradiated and irradiated with such actinic radiation, thereby enabling pattern formation.
In the case where KrF excimer laser is an exposure light source, resins containing as their basic skeletons poly(hydroxystyrene) showing weak absorption in the region of 248 nm are used as a main component. Therefore, such resist compositions have high sensitivity and can form good-quality patterns at high resolution, compared with traditional resist compositions containing naphthoquinonediazide/navolak resin combinations.
However, when light sources of shorter wavelengths, such as ArF exceimer laser (193 nm), are used for exposure, even the chemical amplification resist compositions mentioned above are not satisfactory, because compounds having aromatic groups intrinsically show strong absorption at wavelengths around 193 nm.
Therefore, resist compositions containing resins having alicyclic hydrocarbon structures have been developed as resist adaptable for irradiation with ArF excimer laser.
Patent Document 1 (JP-A-10-254139) describes the use of a solvent mixture of a linear ketone and a solvent selected from a cyclic ketone, a propylene glycol monoalkyl ether acetate or an alkyl 2-hydroxypropionate for the purpose of providing a radiation-sensitive resin composition excelling in transparency to radiation, dry etching resistance, uniformity of film thickness, adhesiveness to substrates, sensitivity, resolution and developing suitability.
Patent Document 2 (JP-A-2002-229192) proposes the use of a specific compound having a cyclic sulfonium structure and a benzene or naphthalene ring as a radiation-sensitive acid generator for the purpose of providing a radiation-sensitive resin composition having not only high transparency to far ultraviolet rays but also high sensitivity, high resolution and excellent pattern profile.
Patent Document 3 (JP-A-2001-142212) discloses the composition containing a specific resin having an alicyclic structure and a certain solvent including propylene glycol monomethyl ether acetate as a resist composition having improvements in sensitivity, resolution, adhesiveness to substrates and pattern edge roughness.
Although various resist compositions have been proposedas mentioned above, it has been desired to further improve performance with respect to the line edge roughness and the defocus latitude common to isolated lines, dense lines and isolated trenches.
The term “line edge roughness” signifies a condition that the edges of the interface between each resist line pattern and a substrate have such a shape as to fluctuate in a direction perpendicular to the line direction owing to resist characteristics. When this line pattern is observed from the position right above, the edges look rough (to an extent of ±dozens nm). This roughness is transferred to the substrate through an etching process, and too rough edges cause impairment of electric characteristics and reduce yield. Thus, the desire to improve line edge roughness is growing as the pattern size becomes finer.
The term defocus latitude refers to the latitude in the matter of deviation from the focus at the time of exposure, and it is desired that patterns of the same size are obtained even when the focus varies to a degree. The expression “defocus latitude common to isolated lines, dense lines and isolated trenches” as used herein means the deviation from the focus that is allowable to the 3 different kinds of fine patterns at the same time, which is different from those to the individual fine patterns. Although the hitherto disclosed resist compositions can yield an improvement in performance of one or two of the foregoing patterns, it is difficult for them to extend the focus deviation allowable to the three patterns at the same time, and so it is to be desired that an improvement in defocus latitude common to isolated lines, dense lines and isolated trenches is made.    [Patent Document 1] JP-A-10-254139    [Patent Document 2] JP-A-2002-229192    [Patent Document 3] JP-A-2001-142212